Finding a file's directory address on a Mac

The desktop is just a subdirectory of the user’s home directory. Because the latter is not fixed, use something like os.path.expanduser to keep the code generic. For example, to read a file called somefile.txt that resides on the desktop, use

import os
f = open(os.path.expanduser("~/Desktop/somefile.txt"))

If you want this to be portable across operating systems, you have to find out where the desktop directory is located on each system separately.

f = open (r"/Users/USERNAME/Desktop/somedir/somefile.txt")

or even better

import os
f = open (os.path.expanduser("~/Desktop/somedir/somefile.txt"))

Because on bash (the default shell on Mac Os X) ~/ represents the user's home directory.